Signal Generator

TMAE 5132G Essentials of Applied Electrical Engineering Laboratory Laboratory # 3 AC Signals, Diodes and Rectifiers Spring 2009

Name: _____________________ PART I. AC Signals, the Oscilloscope and the Function Generator 1. The GFG-8255A Function Generator The front panel of the function generator is shown in Figure 1. This instrument outputs a time-varying periodic voltage signal (OUTPUT connector). By pushing the appropriate buttons on the front panel, the user can specify the following characteristics of the signal: ƒ Shape: square, triangle, or sine waves. These are all mathematical functions of time. ƒ Frequency: inverse of the period of the signal; units are cycles per second (Hz) ƒ Amplitude: peak to peak value of the time-varying component of the signal ƒ DC Offset: constant voltage added to the signal to increase or decrease its mean or average level.

Figure 1. The GFG-8255A Function Generator

In terms of math, a sine wave of frequency f, peak amplitude VP, and DC offset VDC, is written as

v(t) = VP sin (2πf t) + VDC A. To set the frequency of the signal: Select the appropriate button for the frequency range that you want to have. By using the frequency knob tune the value of the desired frequency as shown in the digital display. B. To set a DC offset voltage: Use the knob labeled: OFFSET ADJ. Adjust the desired offset by turning to the right or left this offset knob. You will need the help of the oscilloscope to set the desired offset level. C. To set the amplitude of the signal: Use the know labeled AMPL. Adjust the desired amplitude by turning the AMPL knob.

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TMAE 5132G Essentials of Applied Electrical Engineering Laboratory Laboratory # 3 AC Signals, Diodes and Rectifiers Spring 2009

2. The Hitachi V-1585 Oscilloscope An oscilloscope is a device that graphs voltage versus time. The display shows voltage on the vertical axis as a function of time on the horizontal axis. The user can control the scale of both the time and the voltage axes. The Hitachi V-1585 oscilloscope can accept two voltage inputs (CH1 and CH2) and graph them simultaneously. This is useful because it allows us to compare two signals. For example, we can graph the input signal to a circuit and compare it to the output signal. The front panel of the Hitachi V-1585 oscilloscope is shown in Fig 2.

Figure 2. The Hitachi V-1585 Oscilloscope

PROCEDURE 1.1.- Turn on the oscilloscope with the button labeled POWER. Attach a BNC to alligator cable to the Channel 1 BNC input connector. 1.2.- On the oscilloscope, set the following controls: ƒ CH 1 (volts/div) = 2 ƒ Sec/div = 0.2 ms ƒ Trigger Source = Channel 1 ƒ MODE CH1 1.3.- Turn on the function generator (POWER button pressed). Attach another BNC to alligator cable to the output connector (OUTPUT 50 Ω). Attach the red alligator clips from both cables together. Repeat with the black clips. 1.4.- Configure the Function Generator to output 10 VPP (peak to peak), 1kHz, sinusoidal wave. Mechanical and Electrical Engineering Technology  Georgia Southern University   Page 2 of 8

TMAE 5132G Essentials of Applied Electrical Engineering Laboratory Laboratory # 3 AC Signals, Diodes and Rectifiers Spring 2009 You should now see a sinusoidal wave on the oscilloscope. If not, then ask your instructor or lab assistant for help. The problem may be with some oscilloscope settings, some "buried" function generator settings, or the physical connection. 1.5.- Now, make sure the sinusoidal wave is vertically centered on your scope. Use the VERTICAL POSITION knob (labeled: CH1 POSITION), there is one for each channel. 1.6.- We will use the Sine wave as the standard wave pattern. Adjust the horizontal position of the wave so that the zero amplitude intercepts the vertical axis. This can be adjusted using the HORIZONTAL POSITION knob. 1.7.- You should now have a stable sine wave with an amplitude of 5 volts, a phase shift of 0 degrees, and a frequency of 1 kHz. Measure the Peak-to-Peak amplitude of the waveform, VP-P = ________________ Measure the Peak Voltage, VP = __________________________ Measure the Period and calculate the Frequency of the waveform, indicate the units. Period,

T = __________ (indicate units);

Frequency,

f = __________ (indicate units)

RMS value = ________________ (indicate units) Write the mathematical expression that represents the signal on the oscilloscope _________________________________________________________ equation (1)

1.8.- Given the following equation: v(t) = 5 sin(62832 t ) + 1.5

volts

(2)

What are the following values for the given AC signal: Vp = _______________ volts; Period,

T = __________ (indicate units);

Vp-p = _______________ volts; Frequency,

RMS value = ________________ (indicate units);

f = __________ (indicate units)

DC level: ____________ (indicate units)

RMS + DC = ___________________ (indicate units) Mechanical and Electrical Engineering Technology  Georgia Southern University   Page 3 of 8

TMAE 5132G Essentials of Applied Electrical Engineering Laboratory Laboratory # 3 AC Signals, Diodes and Rectifiers Spring 2009 1.9.- Adjust the function generator to output the waveform in equation 2 a) Measure Vp (peak) and Vpp (peak-to-peak) and record these values: ______________________________________________________________ b) Measure the frequency and DC level of the waveform using the oscilloscope and record these values: ______________________________________________________________ c) Using a DMM (digital multimeter) measure the amplitude of the AC signal and record this value: ______________________________________________________________ d) Comment and explain the difference and relationship between the measurements performed with the oscilloscope and with the DMM: ___________________________________________________________________________

Instructor’s Initials (Part I): _____________ PART II. Diodes and Rectifiers 2.1.- Half-Wave Rectifiers The half-wave rectifier is the simples of the rectifier circuits. It converts AC to pulsating DC by eliminating the negative alternations (or the positive alternations) of the input signal. The circuit in Fig. 3 shows a half-wave rectifier. Fig. 4 shows typical input and output waveforms that are obtained from a half-wave-rectifier.

Figure 3. Circuit diagram of a Half-Wave Rectifier

Figure 4. Typical input and output waveforms of a Half-Wave Rectifier

Procedure. 2.1.1.- Build the circuit shown in Fig. 3. Use a silicon rectifier diode, such as the 1N4001, a transformer and a resistive load of 5.6kΩ. Mechanical and Electrical Engineering Technology  Georgia Southern University   Page 4 of 8

TMAE 5132G Essentials of Applied Electrical Engineering Laboratory Laboratory # 3 AC Signals, Diodes and Rectifiers Spring 2009 2.1.2- Set the oscilloscope to measure in channel one the input voltage, and in channel two the output voltage of your half-wave rectifier. 2.1.3.- Draw next the waveforms as neatly as possible, and fill out the blanks in steps 2.1.4 and 2.1.5.

2.1.4.- For the Input Waveform (channel 1) (indicate the units in all the values) Vp in = ________ Period, T = _____ ;

Frequency, f = _______

Calculate the RMS value, VRMS in = ________ Using the DDM measure the RMS value of the input signal Measured, VRMS in = ________ 2.1.5.- Repeat the readings for the Output Waveform (channel 2) (indicate the units in all the values) Vp out = ___________ Period, T = __________ ;

Frequency, f = _______

Calculate the RMS value, VRMS out = ________ Using a DDM measure the RMS value of the input Measured, VRMS out = ________

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TMAE 5132G Essentials of Applied Electrical Engineering Laboratory Laboratory # 3 AC Signals, Diodes and Rectifiers Spring 2009

2.2.- Full-Wave Center-Tapped Rectifiers The full-wave center-tapped rectifier changes AC to pulsating DC by converting the negative alternations of the input signal to positive alternations. The circuit in Fig. 5 shows a full-wave center-tapped rectifier. Typical input and output waveforms for a full-wave center-tapped rectifier are shown in Fig. 6.

Figure 5. Circuit diagram of a Full-Wave Center-Tapped Rectifier.

Figure 6. Typical input and output waveforms of a Full-Wave CenterTapped Rectifier

Procedure. 2.2.1.- Build the circuit shown in Fig. 5. Use silicon rectifier diodes, such as the 1N4001 , a transformer and a resistive load of 5.6kΩ. 2.2.2.- Set the oscilloscope to measure in channel one the input voltage, and in channel two the output voltage of the full-wave center-tapped rectifier. 2.2.3.- Draw next the waveforms as neatly as possible, and fill out the blanks in steps 2.2.4 and 2.2.5.

2.2.4.- For the Input Waveform (channel 1) (indicate the units in all the values) Vp in = ___________ Period, T = _________ ; Frequency, f = _______ Calculate the RMS value, VRMS in = ________ Using the DDM measure the RMS value of the input signal Measured, VRMS in = ________ Mechanical and Electrical Engineering Technology  Georgia Southern University   Page 6 of 8

TMAE 5132G Essentials of Applied Electrical Engineering Laboratory Laboratory # 3 AC Signals, Diodes and Rectifiers Spring 2009 2.2.5.- Repeat the readings for the Output Waveform (channel 2) (indicate the units in all the values) Vp out = ____________ Period, T = _________ ;

Frequency, f = __________

Calculate the RMS value, VRMS out = ________ Using a DDM measure the RMS value of the input Measured, VRMS out = ________ 2.3.- Full-Wave Bridge Rectifiers The bridge rectifier converts AC to pulsating DC in the same basic way that the full-wave center-tapped rectifier. However, since the bridge rectifier costs much less to produce (the transformer do not need a center tap) and provides much higher output values that the center-tapped rectifier, it is the preferred of the two. The circuit in Fig. 7 shows a bridge rectifier. Typical input and output waveforms for a bridge rectifier have the same form as the full-wave center-tapped rectifier, Fig. 6.

Figure 7. Circuit diagram of a Full-Wave Bridge Rectifier.

Procedure. 2.3.1.- Build the circuit shown in Fig. 7. Use silicon rectifier diodes, such as the 1N4001 , a transformer and a resistive load of 5.6kΩ. 2.3.2.- Set the oscilloscope to measure, in channel one the input voltage, and in channel two the output voltage of the full-wave center-tapped rectifier. 2.3.3.- Draw next the waveforms as neatly as possible, and fill out the blanks in steps 2.3.4 and 2.3.5.

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TMAE 5132G Essentials of Applied Electrical Engineering Laboratory Laboratory # 3 AC Signals, Diodes and Rectifiers Spring 2009 2.3.4.- For the Input Waveform (channel 1) (indicate the units in all the values) Vp in = ___________ Period, T = _________ ;

Frequency, f = _______

Calculate the RMS value, VRMS in = ________ Using the DDM measure the RMS value of the input signal Measured, VRMS in = ________ 2.3.5.- Repeat the readings for the Output Waveform (channel 2) (indicate the units in all the values) Vp out = ___________ Period, T = _________ ;

Frequency, f = _______

Calculate the RMS value, VRMS out = ________ Using a DDM measure the RMS value of the input Measured, VRMS out = ________

Instructor’s Initials (Part II): _____________

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